1. Field of the Invention
The present invention relates to an ink jet apparatus and, particularly, to a void ratio and an average crystal grain diameter of piezoelectric ceramics.
2. Description of the Related Art
Known printer heads include drop-on-demand type ink jet printer heads that utilize piezoelectric ceramics. In these drop-on-demand type ink jet printer heads, the volume of the ink chambers (ink channels) is varied by the deformation of a piezoelectric ceramic. The deformation thereby jets or ejects ink stored in the ink chambers from nozzles as droplets due to a reduction in the volume of the ink chamber. The deformation also causes ink to be introduced into the ink chambers from other ink introduction paths due to an increase in the volume. In print heads using such an ink ejecting device or jet apparatus, ink jet mechanisms are disposed adjacent to each other and droplets of ink are ejected from the ink jet mechanism located at a desired position according to desired print data. Thus, desired characters and images are formed on a sheet or the like disposed in opposing relationship to the ink jet mechanism.
Such an ink jet apparatus is known in U.S. Pat. Nos. 4,879,568, 4,887,100 and 5,016,028, for example. FIGS. 7, 8, 9 and 10 of this application are schematic views showing conventional examples, respectively.
The structure of the conventional example will be specifically described below with reference to FIG. 7 showing a cross-sectional view of the ink jet apparatus. The ink jet apparatus comprises a plurality of side walls 11 and a plurality of ink chambers 12 spaced away from each other in the transverse direction. The ink chambers 12 are formed by bonding a piezoelectric ceramic plate 1 subjected to polarization processing in the direction indicated by the arrow 4 to a cover plate 2 composed of a ceramic material or a resinous material or the like with adhesive layers 3 of an epoxy adhesive or the like interposed therebetween. Each of the ink chambers 12 has a rectangular cross-section and is shaped in an elongated manner. Each of the side walls 11 extends over the overall length of each ink chamber 12. Metal electrodes 13 used for application of drive electric fields are formed on both surfaces, each extending from the upper portion adjacent to each adhesive layer 3 of each side wall 11 to the central portion thereof. All of the ink chambers are filled with ink during operation.
The operation of the conventional example will now be described with reference to FIG. 8 showing a cross-sectional view of the ink jet apparatus. When, for example, an ink chamber 12b in the ink jet apparatus is selected according to desired print data, a positive drive voltage is gradually applied to metal electrodes 13e and 13f and metal electrodes 13d and 13g are grounded. Thus, a drive electric field in the direction indicated by the arrow 14b is exerted on a side wall 11b, whereas a drive electric field in the direction indicated by the arrow 14c is exerted on a side wall 11c. Since, at this time, the drive electric field directions 14b and 14c and a polarization direction 4 meet at right angles to each other, the side walls 11b and 11c are deformed in an outer direction of the ink chamber 12b by a piezoelectric thickness/slip effect. The volume of the ink chamber 12b increases due to the deformation, and hence ink pressure decreases. Thus, the ink is supplied from an ink supply hole 21 (see FIG. 9) to the ink chamber 12b via a manifold 22. When the application of the drive voltage to the metal electrodes 13e and 13f is abruptly stopped, each of the side walls 11b and 11c is rapidly returned to the original position before their deformation. Therefore, the ink pressure in the ink chamber 12b is abruptly raised and a pressure wave is produced. As a result, droplets of ink are ejected or jetted from a nozzle 32 that communicates with the ink chamber 12b.
The structure of the conventional ink jet apparatus and a method of producing it will next be described with reference to FIG. 9, which is illustrative of a perspective view of the ink jet apparatus. A plurality of parallel grooves 12, which form the aforementioned ink chambers, are defined in a piezoelectric ceramic plate 1 subjected to polarization processing by a grinding process using a thin disc-shaped diamond blade. The grooves 12 are identical in depth and parallel to each other substantially over the entire region of the piezoelectric ceramic plate 1. However, the grooves 12 gradually become shallow as they reach an end face 15 of the piezoelectric ceramic plate 1 and merge into grooves 16, which are parallel and shallow in the vicinity of the end face 15. The metal electrodes 13 are formed on the internal faces of the grooves 12 and 16 respectively by sputtering or the like. The metal electrodes 13 are formed only on the upper halves the side faces of the grooves 12. On the other hand, the metal electrodes 13 are also formed on side faces and entire bottom faces of the grooves 16 as seen in FIG. 9.
Further, an ink introduction hole 21 and a manifold 22 are defined in a cover plate 2 made of a ceramic material or a resinous material or the like by grinding or cutting or the like. Next, the surface on the groove processed side of the piezoelectric ceramic plate 1 and the surface on the manifold processed side of the cover plate 2 are bonded to each other by epoxy adhesive or the like so that the respective grooves define the ink chambers having the above shapes. A nozzle plate 31 having nozzles 32 defined therethrough at positions corresponding to the positions of the ink chambers is bonded to the end faces of the piezoelectric plate 1 and the cover plate 2. Further, a substrate 41 having conductive layer patterns 42 formed therein at positions corresponding to the positions of the ink chambers is bonded to the surface of the piezoelectric ceramic plate 1, which is located on the side opposite to the surface on the groove processed side, by epoxy adhesive or the like. Then, the metal electrodes 13 provided on the bottoms of the grooves 16 and the patterns 42 are electrically connected to one another with conductors or lead wires 43 by wire bonding.
The structure of a controller employed in the conventional example will next be described with reference to FIG. 10 showing a block diagram of the controller. The conductive layer patterns 42 formed in the substrate 41 are respectively electrically connected to a corresponding LSI chip 51. Further, a clock line 52, a data line 53, a voltage line 54 and a ground line 55 are also electrically connected to the LSI chip 51. Responsive to a train clock pulse supplied from the clock line 52, the LSI chip 51 decides or determines, based on data that appears on the data line 53, from which nozzle the droplets of ink should be jetted or ejected. Thereafter, the LSI chip 51 applies a voltage supplied from the voltage line 54 to the patterns 42 electrically connected to the driven metal electrodes in the appropriate ink chambers. Further, the LSI chip 51 applies a voltage of 0 at the ground line 55 to the patterns 42 electrically connected to the metal electrodes in the ink chambers that are not to be activated.
However, the relationship between the endurance of the jet and the characteristics of the piezoelectric ceramic material is unclear in the conventional ink jet apparatus described above. Further, the selection of the material is based on the experience of the person in charge of production. Therefore, often the selected piezoelectric ceramic material has poor durability. Hence, the reliability of the ink jet apparatus is low. Further, the ink jet apparatus often has a large variation in drive voltage between the side walls required to stabilize print quality. Thus, the cost of a circuit for stabilizing the print quality increases. Moreover, the drive circuit system is large in structure because of a very high drive voltage, and the cost for taking an insulating measure increases.